Numerous modern electrical devices rely on sensors to provide information about an environment. These sensors can be electrically driven and in most cases consist of some form of transducer which provides an output signal which can be measured. The output signal measured will vary depending on the value of the parameter that is sensed by the sensor. As the sensed parameter changes, so will the sensed output of the transducer. However, a large number of transducers provide output signals that are not directly or linearly proportional to the parameter sensed. For example, in some instances the transducer output may increase exponentially with a linear increase in the sensed parameter, making it difficult to obtain a quick and clear indication of the sensed parameters value. Usually some form of microprocessor or computer is required to provide a scaling function that allows a final linear output to be displayed by the sensor.
Use of a microprocessor in a sensor creates problems if the sensor is to be used in a particularly harsh environment. For example, if the sensor is to be used in an environment where there is a lot of electrical noise, or where it is possible that high voltages may accidentally be applied to the microprocessor, it is likely that the microprocessor will tend to fail or crash frequently. This can be a large problem as the sensor will fail to work correctly or accurately if the microprocessor is continually malfunctioning.
In some transducers, environmental factors such as, for example, ambient temperature, humidity or pressure may also have an effect on the transducer's measured output. In these cases, environmental conditions may change instead of the parameter measured, prompting a change in the transducer's output and hence possibly creating errors in the sensor output. In such situations, environmental conditions also need to be monitored and accounted for when the final result of the transducer is displayed. This is usually done by providing an additional transducer for each environmental condition of concern and imputing a signal from each transducer to the microprocessor used. Provision for these components further complicates the design and manufacture of such sensors.
In most instances, known sensors as discussed above may include a transducer to measure the parameter of interest and a transducer for each environmental condition which has an effect on the output of the first transducer. The output from each transducer is fed through an analog to digital converter and then into a microprocessor which analyzes the signals obtained and takes into account any errors which may be caused by environmental conditions. The microprocessor will then output a digital signal that is linearly proportional to the parameter measured.
In some instances the microprocessor may also be connected to a memory device such as an EPROM which allows information to be stored and supplied to the microprocessor if required. These memory devices are usually configured to contain the machine language instructions (i.e., the program) which is to be executed by the processor. The EPROM is configured to provide these instructions to the processor every time the processor is powered up.
This approach is relatively costly as a separate transducer and an analog to digital converter is required for each environmental condition monitored and also for the parameter measured. This can greatly increase the size and complexity of sensing probes used to place the transducers used in a region of interest. In addition, if the sensors' output is to be sampled at high speed or frequencies, comparatively expensive and fast electrical componentry will also need to be used in the implementation of the sensor.
Recently, sensor users have also found applications for sensors that provide an analog instead of digitized electrical output. In existing devices this could only be obtained if an additional digital to analog converter was placed at the output of the sensor. However this approach again increases the cost of the sensor and further reduces the speed at which the sensors' output can be updated.
An improved sensor that could be implemented with limited and inexpensive components would be of greater advantage over the prior art. An improved sensor that only required one transducer yet still took account of environmental conditions affecting the transducers operation would also be of great advantage over the prior art. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.